#include <fstream>

using namespace std;


inline unsigned long long int find_five(long p) {
     long i=0,zero=0,j;
     short cont;
     while(p>0) {
          cont=1;
          i+=5;
          j=i/5;
          verifica:
          if(j%5==0) {
               cont++;
               j/=5;
               goto verifica;
          }
          p-=cont;
          zero+=cont;
     }
     return i;
}

int main() {
     long p;
     ifstream f("fact.in");
     f>>p;
     f.close();
    ofstream g("fact.out");
      g<<find_five(p);
     g.close();
     return 0;
}